Humidity determining device and environmental tester including the same

A humidity determining device configured to determine a humidity in a test chamber, the humidity in the test chamber having a true value, the humidity determining device comprising:

• a first humidity determining section configured to determine the humidity in the test chamber, the first humidity determining section having a humidity determining performance which changes in amount of deviation relative to the true value with time due to a reaction of the first humidity determining section with a chemical substance contained in the test chamber;
• a second humidity determining section disposed near the first humidity determining section and configured to determine the humidity in the test chamber, the second humidity determining section having a humidity determining performance which changes in amount of deviation relative to the true value with time due to a reaction of the second humidity determining section with the chemical substance, wherein the humidity determining performance of the first humidity determining section changes in amount of deviation relative to the true value with time differently from the changes in amount of deviation relative to the true value with time of the humidity determining performance of the second humidity determining section;
• and
• a controller configured to receive a first humidity value determined by the first humidity determining section and a second humidity value determined by the second humidity determining section, wherein
• the controller is configured to compute a difference value between the first humidity value and the second humidity value and to output, when a net difference in the amount of deviation of the first humidity determining section and the amount of deviation of the second humidity determining section relative to the true value is greater than a predetermined reference value, an anomaly signal indicating that the humidity determining performance of at least one of the first humidity determining section or the second humidity determining section has been reduced.